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diff --git a/absl/flags/internal/registry.h b/absl/flags/internal/registry.h
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+//
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_FLAGS_INTERNAL_REGISTRY_H_
+#define ABSL_FLAGS_INTERNAL_REGISTRY_H_
+
+#include <functional>
+#include <map>
+#include <string>
+
+#include "absl/base/macros.h"
+#include "absl/flags/internal/commandlineflag.h"
+
+// --------------------------------------------------------------------
+// Global flags registry API.
+
+namespace absl {
+inline namespace lts_2019_08_08 {
+namespace flags_internal {
+
+// CommandLineFlagInfo holds all information for a flag.
+struct CommandLineFlagInfo {
+  std::string name;           // the name of the flag
+  std::string type;           // DO NOT use. Use flag->IsOfType<T>() instead.
+  std::string description;    // the "help text" associated with the flag
+  std::string current_value;  // the current value, as a std::string
+  std::string default_value;  // the default value, as a std::string
+  std::string filename;       // 'cleaned' version of filename holding the flag
+  bool has_validator_fn;  // true if RegisterFlagValidator called on this flag
+
+  bool is_default;  // true if the flag has the default value and
+                    // has not been set explicitly from the cmdline
+                    // or via SetCommandLineOption.
+
+  // nullptr for ABSL_FLAG.  A pointer to the flag's current value
+  // otherwise.  E.g., for DEFINE_int32(foo, ...), flag_ptr will be
+  // &FLAGS_foo.
+  const void* flag_ptr;
+};
+
+//-----------------------------------------------------------------------------
+
+void FillCommandLineFlagInfo(CommandLineFlag* flag,
+                             CommandLineFlagInfo* result);
+
+//-----------------------------------------------------------------------------
+
+CommandLineFlag* FindCommandLineFlag(absl::string_view name);
+CommandLineFlag* FindRetiredFlag(absl::string_view name);
+
+// Executes specified visitor for each non-retired flag in the registry.
+// Requires the caller hold the registry lock.
+void ForEachFlagUnlocked(std::function<void(CommandLineFlag*)> visitor);
+// Executes specified visitor for each non-retired flag in the registry. While
+// callback are executed, the registry is locked and can't be changed.
+void ForEachFlag(std::function<void(CommandLineFlag*)> visitor);
+
+//-----------------------------------------------------------------------------
+
+// Store the list of all flags in *OUTPUT, sorted by file.
+void GetAllFlags(std::vector<CommandLineFlagInfo>* OUTPUT);
+
+//-----------------------------------------------------------------------------
+
+bool RegisterCommandLineFlag(CommandLineFlag*);
+
+//-----------------------------------------------------------------------------
+// Retired registrations:
+//
+// Retired flag registrations are treated specially. A 'retired' flag is
+// provided only for compatibility with automated invocations that still
+// name it.  A 'retired' flag:
+//   - is not bound to a C++ FLAGS_ reference.
+//   - has a type and a value, but that value is intentionally inaccessible.
+//   - does not appear in --help messages.
+//   - is fully supported by _all_ flag parsing routines.
+//   - consumes args normally, and complains about type mismatches in its
+//     argument.
+//   - emits a complaint but does not die (e.g. LOG(ERROR)) if it is
+//     accessed by name through the flags API for parsing or otherwise.
+//
+// The registrations for a flag happen in an unspecified order as the
+// initializers for the namespace-scope objects of a program are run.
+// Any number of weak registrations for a flag can weakly define the flag.
+// One non-weak registration will upgrade the flag from weak to non-weak.
+// Further weak registrations of a non-weak flag are ignored.
+//
+// This mechanism is designed to support moving dead flags into a
+// 'graveyard' library.  An example migration:
+//
+//   0: Remove references to this FLAGS_flagname in the C++ codebase.
+//   1: Register as 'retired' in old_lib.
+//   2: Make old_lib depend on graveyard.
+//   3: Add a redundant 'retired' registration to graveyard.
+//   4: Remove the old_lib 'retired' registration.
+//   5: Eventually delete the graveyard registration entirely.
+//
+// Returns bool to enable use in namespace-scope initializers.
+// For example:
+//
+//   static const bool dummy = base::RetiredFlag<int32_t>("myflag");
+//
+// Or to declare several at once:
+//
+//   static bool dummies[] = {
+//       base::RetiredFlag<std::string>("some_string_flag"),
+//       base::RetiredFlag<double>("some_double_flag"),
+//       base::RetiredFlag<int32_t>("some_int32_flag")
+//   };
+
+// Retire flag with name "name" and type indicated by ops.
+bool Retire(FlagOpFn ops, FlagMarshallingOpFn marshalling_ops,
+            const char* name);
+
+// Registered a retired flag with name 'flag_name' and type 'T'.
+template <typename T>
+inline bool RetiredFlag(const char* flag_name) {
+  return flags_internal::Retire(flags_internal::FlagOps<T>,
+                                flags_internal::FlagMarshallingOps<T>,
+                                flag_name);
+}
+
+// If the flag is retired, returns true and indicates in |*type_is_bool|
+// whether the type of the retired flag is a bool.
+// Only to be called by code that needs to explicitly ignore retired flags.
+bool IsRetiredFlag(absl::string_view name, bool* type_is_bool);
+
+//-----------------------------------------------------------------------------
+// Saves the states (value, default value, whether the user has set
+// the flag, registered validators, etc) of all flags, and restores
+// them when the FlagSaver is destroyed.
+//
+// This class is thread-safe.  However, its destructor writes to
+// exactly the set of flags that have changed value during its
+// lifetime, so concurrent _direct_ access to those flags
+// (i.e. FLAGS_foo instead of {Get,Set}CommandLineOption()) is unsafe.
+
+class FlagSaver {
+ public:
+  FlagSaver();
+  ~FlagSaver();
+
+  FlagSaver(const FlagSaver&) = delete;
+  void operator=(const FlagSaver&) = delete;
+
+  // Prevents saver from restoring the saved state of flags.
+  void Ignore();
+
+ private:
+  class FlagSaverImpl* impl_;  // we use pimpl here to keep API steady
+};
+
+}  // namespace flags_internal
+}  // inline namespace lts_2019_08_08
+}  // namespace absl
+
+#endif  // ABSL_FLAGS_INTERNAL_REGISTRY_H_